1. Field of the Invention
This invention relates to an information reproducing apparatus for reproducing information from an information recording medium having a concentric or spiral information track on which the information is recorded.
2. Description of the Prior Art
Since the information recording medium of a concentric or spiral information track on which the information is recorded, has a high recording density, an information reproducing apparatus generally requires position controls for accurate tracking and focusing or the like. Such information recording mediums are already well known, such as the optical video disc, the digital audio disc, the data file, the no-groove electrostatic capacitance system video disc and the magnetic disc of high density and of data surface servo, which perform position control for tracking or focusing during the reproduction, thereby enabling recording and reproduction at a high density. However, when the information track disappears due to a defect on the recording medium or a large noise enters into a position control signal, the tracking or focusing control would not work, thereby, causing the track to jump to the adjacent information track. Especially, the optical digital audio disc, in which the travelling velocity of information track is slow, has a remarkable tendency to jump. In order to solve this problem, the method has hitherto been proposed which detects the defect on the information record medium and holds, during tracking the defective portion, a low frequency component value just before the defective portion.
Usually, when the defect is detected, the time delay inevitably exists, whereby the large noise often remains in the position control signal when the tracking enters the defective portion. Hence, the noise will increase tracking errors in the subsequent defective portion to result in a track jump occurring.